There’s plenty to learn from a frozen water balloon, starting with the patterns of bubbles—or lack thereof—in the ice.
The water in an ice balloon freezes from the outside in. As the water freezes, it creates pure crystals of water, which are clear. Meanwhile, impurities such as air or minerals are left behind in the liquid, where they concentrate until they come out of solution as bubbles. One bubble can seed a neighboring bubble, creating a radial chain of bubbles. Since bubbles scatter light of all wavelengths, they give the ice balloon a white, opaque center (see photo below).
When the balloon comes out of the freezer, it’s often at a temperature of 0°F (-18°C), much colder than the freezing point of 32°F (0°C). At these cold temperatures, water vapor in the air can freeze onto the balloon, creating a layer of frost. When the surface of the balloon warms to the freezing point, a visible film of water appears on the surface and the frost disappears.
Salt on the balloon will cause the ice to melt, even at temperatures below freezing. In any ice/water combination, there is an ongoing back-and-forth in which some liquid water molecules are freezing while some solid water (ice) is melting. Ions of sodium and chlorine from the salt get in the way of ice-crystal formation, turning the back-and-forth into more of a one-way street in which more ice melts then freezes.
As the salty liquid water flows down the balloon, it begins to form meandering streams, just as rivers do (see photo below). As in rivers, the meanders shift over time, responding to subtle changes in flow and channel shape.
Most substances shrink as they cool, but water is a notable exception, freezing into hexagonal crystalline structures that take up about 10 percent more space than liquid water. This increased volume translates into lower density, causing ice to float. A solid ice balloon placed in water displaces its weight in water—this is Archimedes’ principle—with 10 percent of the ice balloon above the surface and 90 percent below.